1. Field of the Invention
This invention is related to medical formulations used to treat and protect the central nervous system and methods of using those formulations. In particular, the invention relates to neuroprotective compositions and methods using those compositions to protect the brain or minimize lasting damage.
2. Background Information
Most Central Nervous System (CNS) injuries, including stroke, trauma, hypoxia-ischemia, multiple sclerosis, seizure, infection, and poisoning directly or indirectly involve a disruption of blood supply to the CNS, and share the same common pathologic process, that is: rapid cerebral edema leading to irreversible brain damage, and eventually to brain cell death.
One common injury to the CNS is stroke, the destruction of brain tissue as a result of intracerebral hemorrhage or infarction. Stroke is a leading cause of death in the developed world. It may be caused by reduced blood flow or ischemia that results in deficient blood supply and death of tissues in one area of the brain (infarction). Causes of ischemic strokes include blood clots that form in the blood vessels in the brain (thrombus) and blood clots or pieces of atherosclerotic plaque or other material that travel to the brain from another location (emboli). Bleeding (hemorrhage) within the brain may also cause symptoms that mimic stroke.
CNS tissue is highly dependent on blood supply and is very vulnerable to interruption of blood supply. Without neuroprotection, even a brief interruption to the blood flow to the central nervous system can cause neurologic deficit. The brain is believed to tolerate complete interruption of blood flow for a maximum of about 5 to 10 minutes.
It has been observed that after blood flow is restored to areas of the brain that have suffered an ischemic injury, secondary hemodynamic disturbances have long lasting effects that interfere with the ability of the blood to supply oxygen to central nervous system tissues. This has been called the xe2x80x9cno-reflowxe2x80x9d phenomenon.
Similarly, interruption of the blood flow to the spinal cord, for even short periods of time, can result in the xe2x80x9cno-reflowxe2x80x9d phenomenon leading to paralysis.
Recognition of the xe2x80x9cischemic penumbra,xe2x80x9d a region of reduced cerebral blood flow in which cell death might be prevented, has focused attention on treatments that might minimize or reverse brain damage when administered soon after stroke onset. Enlargement of infarct volume is determined by changes in metabolism caused by initiation of the ischemic cascade. This cascade involves energy supply failure, membrane depolarization, release of neurotransmitters (including glutamate in large amounts), accumulation of intracellular calcium, increased production of nitric oxide and free radicals, development of cellular edema, and finally, cell death. Each step along the ischemic cascade offers a potential target for therapeutic intervention. To date, several classes of neuroprotective compounds have been investigated in phase 3 trials for acute stroke. They have included calcium channel antagonists, N-methyl-D-aspartate (NMDA) receptor antagonists, free radical scavengers, anti-intercellular adhesion molecule 1 antibody, GM-1 ganglioside, [gamma]-aminobutyric acid agonists, and sodium channel antagonists, among others. All of the trials have yielded disappointing efficacy results and some showed safety problems, including increased mortality or psychotic effects, which resulted in their early termination.
A neuroprotectant is a substance that can increase the tolerance of CNS tissues to injury or disruption of blood supply. A broad spectrum of compounds with disparate mechanisms of action have been considered, from oxygen free radical scavengers, calcium channel blockers and glutamate receptor antagonists to monoclonal antibodies that attempt to curtail inflammatory cascades occurring in cerebral injuries. Although several of these agents seems have been effective in vitro, very few have shown real advantages in in vivo testing or clinical studies. These agents are directed to molecular mechanisms of nerve cell injuries, but they do not address the one injury path common to all CNS injuries, cerebral edema.
Current treatments for stroke include recombinant tissue plasminogen activator (rt-PA), a thrombolytic agent, that has been shown to be effective dissolving clots to restore blood flow to injured areas of the brain if used within 3 hours after the onset of the stroke.
U.S. Pat. No. 5,755,237 to Rodriguez discloses acetazolamide for the treatment of brain edema. Acetazolamide can inhibit cerebrospinal fluid production, but administering of acetazolamide alone does not have a neuroprotective effect.
A series of patents, U.S. Pat. Nos. 4,981,691, 4,758,431, 4,445,887, 4,445,500, and 4,393,863 to Osterholm disclose a fluorocarbon solution for treatment of hypoxic-ischemic neurologic tissue.
Many proposed neuroprotective agents such as oxygen free radical scavengers, NMDA receptor antagonists, and apoptosis inhibitors seem to have measurable effect in vitro. However, during in vivo study and clinical trials, these agents do not show a neuroprotective effect.
I have now found that draining the cerebrospinal fluid (CSF) from the central nervous system, and replacing the CSF with an oil combined with an amphipathic lipid to adsorb edematous liquid in the CNS prevents cerebral edema. Elimination of this cerebral edema prevents the onset of the no-reflow phenomenon, enabling blood to reperfuse CNS tissue after significant periods of ischemia. Preventing the continuing hemodynamic disturbance, the no-reflow phenomenon, protects the CNS tissue making it resistant to injuries, and lengthening the therapeutic window for all other therapies.
This invention provides compositions and methods for protecting brain and spinal cord from injuries resulting from interruption of blood flow. Compositions according to this invention may be used to treat neurological disorders, such as stroke, hypoxia-ischemia, hemorrhage, trauma, multiple sclerosis, seizure, infection, or poisoning. The compositions are also useful during open-heart surgery, neurosurgery, shock, or other procedures where blood flow to the CNS is interrupted.
There are many advantages to the compositions and method I have discovered.
One advantage is improving the efficacy of existing treatments for stroke, head trauma, and other invasive procedures. Administering an effective neuroprotectant agent according to this invention will increase the therapeutic window, the period of time in which any other treatment, including thrombolytic agents can be used. For example, tPA, the only FDA approved medication for stroke, is a thrombolytic agent targeted on dissolving the blood clots that led to the stroke. tPA is not targeted on, and has no observed effect on cerebral edema. tPA is now only approved for use within 3 hours after onset of ischemia. When used in combination with the instant composition and method, the therapeutic window for all known treatments now used for supporting CNS tissue will be much longer.
This invention, if combined with other known techniques such as controlled hypothermia, may significantly increase the length of time a patient can tolerate cerebral ischemia. A patient treated according to this invention may survive invasive procedures performed on any part of the CNS without injury, including areas of the brain that have not been surgically accessible prior to this invention. Additionally, procedures that require interruption of the blood flow, such as heart surgery, repair of aortic aneurysm, or any other surgery where systemic blood circulation is interrupted can be performed with increased safety.
The compositions and methods I have invented extend the therapeutic window for successfully recovering from a stroke or cardiac arrest from mere minutes to hours. In addition, this compositions and method are useful for screening neuroprotective agents developed based on other mechanisms.
The formulations I have found that have a neuroprotective effect are organic solutions. These solutions include an amphipathic lipid in an oil. Optionally, the treatment solution may include one of more of the following: an osmotic dehydrant; a compound that may supply energy to a cell; a compound that decreases the metabolism of the cell; or an agent that suppresses the production of cerebrospinal fluid.
I have found the formulations I have used are effective when it is applied to the subarachnoid spaces after the cerebrospinal fluid has been removed from the subarachnoid spaces. These methods are effective to treat injured central nervous system tissue or to protect that tissue from continuing damage after injury of trauma.
The compositions and methods are effective to treat stroke.
The compositions and methods enhance the effectiveness of neuroprotective agents.
The compositions and methods can extend to the therapeutic window of thrombolytic agents such as recombinant tissue plasminogen activator.
In ischemic injury, CSF has a toxic effect facilitating cerebral edema, blocking cerebral blood flow and collateral circulation to damaged nerve tissue, the no-reflow phenomenon. This failure of circulation results in continuing damage to CNS tissue after the interruption of blood flow is reversed. Restoration of blood flow to the affected area of the CNS after a period of ischemia as short as six minutes does not result in blood re-flow to the affected CNS tissue. After blood flow to the CNS is interrupted, CSF infiltrates the CNS tissue causing edema. The edematous CSF remains in the CNS tissue preventing blood re-flow into the affected tissues after blood circulation is restored. As the duration of blood flow interruption increases, the edema spreads throughout the CNS tissue causing additional damage in an ischemic cascade.
In the adult human, the average intra-cranial volume is about 1700 ml. The volume of the brain is approximately 1400 ml; CSF volume ranges from about 52 to about 160 ml (mean 140 ml), and blood volume is about 150 ml. Thus, the CSF occupies about 10 percent of the intra-cranial and intra-spinal volume.
The choroid plexuses are the main sites of CSF formation. The average rate of CSF formation is about 21 to 22 ml/hr, or approximately 500 ml/day. The CSF as a whole is renewed four or five times daily. CSF formation is related to intracranial pressure. When the intracranial pressure is below about 70 mm H2O, CSF is not absorbed, and production increases. CSF is a very dilute aqueous solution with a low colloidal osmotic pressure.
The CSF has a mechanical function. It serves as a kind of water jacket for the spinal cord and brain, protecting them from trauma and acute changes in venous blood pressure. The CSF provides buoyancy and shock absorption, so that brain and spinal cord float in a CSF pool. CSF does not appear to be necessary to brain or spinal cord metabolism. However, during ischemic episodes, CFS has a toxic effect by facilitating cerebral edema and the resulting in no-reflow phenomenon after disruption of blood flow to CNS tissue.
The mechanism of injury leading to brain edema is not fully understood. However, when the blood flow to the nerve cells has been interrupted, there is a shift of electrolytes and fluids across the nerve cell membranes. Swelling (edema) occurs when the CNS tissue absorbs fluid such as CSF. When injury occurs, CSF readily penetrates CNS tissues. Additionally the edema may cause collapse of blood vessels within the affected tissue. Ischemic injury to the central nervous system may be either global, in the case of general failure of blood circulation after a cardiac arrest, or local over an area of any size after for example, a head trauma, an intra-cerebral hemorrhage, or a stroke. It is known however, that if cerebral edema induced by ischemia of whatever dimension is not controlled, then the edema spreads and the severity of the resultant injury rapidly increases.
In order to prevent cerebral edema, and the irreversible effects that occur after ischemia, the CSF is withdrawn from the affected area of the CNS. It is preferred to completely remove all CSF from the injured area. It is advantageous to completely remove all CSF from the CNS. However, it is very difficult, almost impossible, mechanically to remove CSF completely from the subarachnoid spaces or the brain surface because the brain contour is very complex with many sulci, gyri and pools. Even if the intra cranial pressure is mechanically reduced below zero, surface tension and capillary forces retain CSF in the spaces between the dura and the cerebral surface. Similarly, in edematous cerebral tissue, CSF is retained in Virchow-Robin space (or extra cellular space), including the spaces surrounding smaller vessels that penetrate into the brain from the periphery.
Mechanically withdrawing CSF alone is not sufficient to achieve the neuroprotective effect. This residual aqueous CSF can significantly decrease the protective effect because it is a continued source of edematous fluid that can cause delayed or recurring injury. Removing CSF from the edematous tissue is necessary to prevent the occurrence of the no-reflow phenomenon. CSF remaining in the area of edema exerts pressure on blood vessels in the area, preventing blood flow from reaching the affected CNS tissues even after blood flow is restored.
In this method, the CSF is withdrawn from the cerebral circulation through one or more cannulas. For maximum CNS tissue protection, two small holes are drilled on the skull, the dura is punctured, and a cannula is placed in through the dura into the subarachnoid spaces. Additional cannulas may be inserted into the lateral cerebral ventricles, the lumbar theca, and the cisterna magna. CSF can be removed from any or all of these locations to remove edematous fluid, or to reduce and prevent edema.
For a spinal cord injury, a cannula may be placed through a puncture in the lumbar theca or cisterna magna. Optionally, two cannulas may be used.
CSF pressure control has been used for protecting spinal cord during aortic surgery. Controlling the pressure of CFS, in particular, maintaining a pressure lower than the central venous pressure can be advantageous in protecting the spinal cord from injury during aortic surgery. However, such pressure control does not achieve the neuroprotective effect in the case of more general ischemia. Removing CSF from the spinal cord""s subarachnoid space is relatively easier (compared with from brain) because of spinal cord""s more simple contour. However, simple withdrawal of CSF even under controlled conditions in thoraco-aortic surgery, is not predictably effective protecting CNS tissue.
Complete removal of CSF reduces or eliminates edema in the CNS, but removal alone is not sufficient to protect the CNS from damage. As discussed above, the CSF performs a support and shock absorbing function, accordingly some liquid medium is necessary to support the CNS tissues in the body. In addition to providing a support media for the CNS tissues, it is important to maintain a controlled level of pressure within the CNS. Carefully controlling the pressure is necessary to prevent severe headache, or further disruption of blood flow.
In the instant method, the CSF (usually 50-200 ml) is withdrawn from the cranium and spinal cord. As discussed above, it is advantageous to completely remove the CSF, but for a localized injury, or for a spinal cord injury, beneficial effects can be achieved upon removal of a lesser volume of CSF. If it is not possible to remove the CSF, from the injured site, the CSF may be displaced with a treatment oil.
After the CSF has been withdrawn, an equal volume of treatment oil is injected into the space surrounding the affected CNS. This treatment oil performs the mechanical functions of the CSF, i.e. insulating the brain tissue from shock and providing a media to support the CNS organs buoyantly. Because the volume of treatment inserted into the cranium or the spinal cord is approximately equal to the volume of the CSF withdrawn, the intercranial pressure is stabilized and hernia or hemorrhage are prevented. The treatment oil supports the CNS tissues. It also coats the surfaces of the CNS tissue forming a lipid barrier that inhibits the penetration of CSF into the CNS tissues. The surfaces of the CNS tissues have a greater affinity for the non-polar oil than for the aqueous CSF. Because the density of the treatment oil is less than that of CSF, rotating the body about an axis, or elevating the head, will allow the treatment oil to cover all CNS tissue surfaces.
The treatment oil is an organic solution including an amphipathic lipid in oil. Other ingredients may be added including agents to suppress production of CSF, or other therapeutic agents. The treatment oil has a density less than that of water, but sufficient to support the organs of the CNS buoyantly. The treatment oil should have a physiologic pH.
The oil can be any non-aqueous, liquid, low viscosity material that is soluble in organic solvents but immiscible with water. Hydrocarbon oils and silicone oils are effective. Soybean oil, cod liver oil, vitamin E oil, olive oil, canola oil, corn oil, mineral oil, and mixtures of these oils in any concentration ratio may be used. Oils containing high concentrations of omega-3 fatty acid oils such as fish oils or their mixtures can be used, and may be advantageous because of their anti oxidant properties. However, any stable, low viscosity, non-aqueous fluid can be used, including fluorocarbons such as the Fluorinert(copyright) compounds manufactured by 3M Company of St. Paul Minn.
While the oil alone can have significant effect, I have found that adding an amphipathic lipid to the oil compositions enhances the neuroprotective effect. The amphipathic lipid is generally any organic molecule having both a polar functional group, such as a carbonic acid, phosphate, or other polar functional group at one end, and a non-polar, hydrocarbon functional group at another end. Examples of the amphipathic agents used in this composition include fatty acids, phosphoglycerides, sphingomyelins, glycolipids, cholesterol, cholesterol hemisuccinate, sphingolipids, and cerebrosides. Surface active agents, such as, Triton X-100 and didodecyldimethylammonium bromide, may be also used. Lecithin, a phospholipid that is a constituent of cell membranes, has been shown to be effective. However, any amphipathic lipid added to the oil is effective.
To make the treatment oil, the amphipathic lipid is added in a concentration of from about 0.1 to about 40 grams to 100 ml of the oil. The concentration used is limited only by the solubility of the amphipathic lipid in the particular oil used. Concentrations of from about 0.1 to about 10 grams of amphipathic lipid per 100 ml of can be easily prepared. Concentrations of about 1 gram of amphipathic lipid per 100 ml of oil can be used for direct comparison of the relative effect of any amphipathic lipid in any particular oil.
Treatment oil with the amphipathic lipid draws edematous CSF fluids away from the CNS tissue and into the treatment oil. The amphipathic component of the composition acts as a hook to pull out the water from Virchow-Robin space in the edematous tissue. This reduces the extent of any existing edema and prevents the spread of the edema. Additionally, the treatment oil with amphipathic lipid compositions is effective reducing edema when administered after the onset of edema. The amphipathic lipid improves the efficacy of the treatment oil under most circumstances, particularly when administered some time after the onset of edema.
The effect of this treatment oil/amphipathic lipid composition can be achieved over a period of several hours. In some cases, a substantial period of time is required for withdrawal of edematous fluid from the cells in the injured area. In addition, it may take a substantial time for injured CNS tissue to recover. Because of the lengthy periods of time, recurrent and delayed CSF toxicity are a significant concern. Suppressing production of CSF during treatment can be advantageous.
There are many known agents that inhibit production of CSF. These include Furosemide (20-200 mg every 4-6 hours), and acetazolamide (0.25-2 g every 4-12 hours). Other agents known to suppress formation of CSF include: beta blocking agents such as isopranolol, and timolol maleate; and calcium channel blockers such as brinzolamide, dorzolamide, methazolamide, sezolamide, lantanoprost, and bis (carbonyl) amidothiadiazole sulfonamides; and carbonic acid anhydrase inhibitors such as triamterene, spironolactone, thiazides, and, Na and K-ATPase inhibitors. This CSF inhibiting agent can be administered intravenously or orally in cases where circulation to the brain has not been impaired, or by direct injection to subarachnoid space, either in combination with the treatment oil, or alone to inhibit new CSF production.
While these agents are known to lower CSF production, these agents alone do not have a neuroprotective effect in an ischemic incident. Lowering the intracranial pressure or stopping the CSF production without removing the edematous CSF from the subarachnoid spaces does not achieve a neuroprotective effect. The CSF in the cranial cavity at the time blood flow is interrupted is enough to cause the cerebral edema and tissue damage.
The compositions and methods herein can be advantageously combined with any of the compositions used to treat stroke or other neurological deficiencies including: calcium channel blockers such as Nimodipine, and Flunarizine; calcium chelators, such as DP-b99; potassium channel blockers; Free radical scavengersxe2x80x94Antioxidants such as Ebselen, porphyrin catalytic antioxidant manganese (III) meso-tetrakis (N-ethylpyridinium-2-yl) porphyrin, (MnTE-2-PyP (5+)), disodium 4-[(tert-butylimino) methyl] benzene-1,3-disulfonate N-oxide (NXY-059), N:-t-butyl-phenylnitrone or Tirilazad; GABA agonists including Clomethiazole; GABA receptor antagonists, glutamate antagonists, including AMPA antagonists such as GYKI 52466, NBQX, YM90K, YN872, ZK-200775 MPQX, Kainate antagonist SYM 2081, NMDA antagonists, including competitive NMDA antagonists such as CGS 19755 (Selfotel); NMDA channel blockers including Aptiganel (Cerestat), CP-101,606, Dextrorphan, destromethorphan, magnesium, metamine, MK-801, NPS 1506, and Remacemide; Glycine site antagonists including ACEA 1021, and GV 150026; polyamine site antagonists such as Eliprodil, and Ifenprodil; and adenosine receptor antagonists; Growth factors such as Fibroblast Growth Factor (bFGF), Glial cell line derived neurotrophic factor (GDNF), brain derived neurotrophic factor, insulin like growth factor, or neurotrophin; Leukocyte adhesion inhibitors such as Anti ICAM antibody (Enlimomab) and Hu23F2G; Nitric oxide inhibitors including Lubeluzole; opiod antagonists, such as Naloxone, Nalmefenem, Phosphatidyleholine precursor, Citicoline (CDP-coline); Serotonin agonists including Bay x 3072; Sodium channel blockers such as Fosphenytoin, Lubeluzole, and 619C89; Potassium channel openers such as BMS-204352; anti-inflamatory agents; protein kinase inhibitors, and other agents whose mechanism of action is unknown or uncertain including: Piracetam and albumin. Other active agents, that provide energy to cells, such as ATP, co-enzyme A, co-enzyme Q, or cytochrome C may be added. Similarly, agents known to reduce cellular demand for energy, such as phenytoin, barbital, or lithium may be added to the oil.
The compositions and methods can be combined with and enhance the efficiency of thrombolytic agents such as:
recombinant tissue plasminogen activator (rtpA), streptokinase, and tenecteplase in dissolving thrombosis in management of stroke or myocardial infarction.
Osmotic dehydrants, such as mannitol, sorbitol, or glycerin may assist in removal of CSF from edenateous tissue.